Throttle valve for machine tool control



Sept. 4, 1945. I m 2,384,078

THROTTLE VALVE FOR MACHINE TOOL CONTROL Filed March 5, 1941 INVENTOR firm/KW 6 mm:

incorporation in a unitary control panel.

Patented Sept. 4, 1945 THROTTLE VALVE FOR MACHINE TOOL CONTROL Frank W. Curtis, Springfield, Masa, assig'nor to Van Norman Company, a corporation of Massachusetts Application March 5,1941, Serial No. 381,780

1 Claim.

This invention relates to a throttle valve particularly intended for regulating the feed speed of hydraulically operated machine tools such as milling machines. ne object is to provide a throttle which can control with great accuracy the feed rate of a machine tool. A further object is to provide an improved throttle which can be graduated in uniformly spaced divisions corresponding to equal increments in speed; or alternatively can be adapted to give speeds increasing in a geometrical or other proportion as the valve is turned through equal increments. A further object is to provide a throttle valve which may be clamped in position after being set. A further object is to provide a throttle valve adapted for Additional objects will appear from the following description and claim;

Referring to the drawing,

Fig. l is a sectional view through a valve embodying the invention;

Fig. 2 is a developed view of the valve sleeve;

Fig. 3 is a developed view of the valve plug;

Fig. 4 is a diagram showing how the area of the port opened is increased as the throttle is turned;

Fig. 5 is a similar diagram showing a modiiication: and

Fig. 6 is a perspective detail of that modification.

Mechanically the throttle is of great simplicity.

'Against a shoulder ill in a bore ll formed in' the casing I2 is located a sleeve l3, preferably formed separate from the casing to facilitate hardening and lapping. Between the end of this sleeve and a cylindrical flange ii on a cap I! secured to the casing is a radial flange ll forming part of the valve plug ll. The plug is thus positioned with great accuracy longitudinally of vthe sleeve. An oil seal ll surrounds the plug adjacent the shoulder II. The stem is of the plug projects through the casing and is provided with serrations 20 forming a sliding coupling with complementary serrations in a combined dial and handle II. Beyond the dial the stem I0 is threaded at 22 to receive a locking nut 23. By tighteningthis nut the dial is pressed against the wall of the casing 12, firmly holding the plug in the position in which it is adjusted.

The sleeve II is provided with an inlet port 25 and an outlet port 20, here shown as diametrically opposite although this relationship is. not important. In the plug is a groove having an axially inclined portion 21 and a portion 20 connectlog therewith and lying in the same plane as the port. As the valve plug is rotated the inclined part 21 oi the groove gradually rides over the edge of the inletport. and as the angle of inclination can be made as gentle as desired the change in speed as the valve plug is turned can be made very gradual and accurate. Hie action has been shown in Fig. 4, where for the NW of clarity the port has been shifted along the groove rathenthan vice versa.

The shape 01' the groove depends upon two factors, which can be combined to produce whatever over-all eii'ect may he wished. The ilrst of these is the relation between volume or the flow of liquid through the throttle and the area of port exposed. 0n the lower range, which is the most important, the flow will vary about proportion to the 0.7 power oi the exposed area. and this law may be assumed with reasonable accuracy for the workable range. The exact pro portion will vary somewhat as the size and shape or the area changes, but the now in general can be expressed with reasonable accuracy as being proportional to some power of the area in the range of 0.5 to 0.7. Stating this inversely. in

. order to keep constant increments of flow be',

tween uniform increments of displacement of the valve, the area uncovered should be proportional to the 1.4 power of the amount of rotation of the plug.

Using these values it is possible to proportion the pitch of the generally helical groove TI to give whatever type or spacing of the graduations on the dial may be desired. In Fig. 3 has been shown an arrangement in which uniformly spaced graduations on the dial will produce proportional changes in the volume 01' flow oi the fluid. In the case shown suitable proportions may be given as an example for a valve plug of 1%" diameter. It should be noted that the groovef-has' been formed in short helical segments or diflering pitch, giving an approximation only to the smooth theoretical curve but facilitating the machining in many cases and giving sumciently accurate results for most practical purposes. In this case inclination of the groove is 0.015" in the first 40: 0.035- in the next 50; and 0.081" in the next 40.

Instead of changing the pitch of the groove to control the area oi port exposed a helical groove may be used' and a port of specially designed shape employed. This is oi particular.

utility in cases where it is desired to preserve especial accuracy in the setting for the lower flows. one form of port opening for this mm is shown at II in Figso and 0, which cooperates the dial it is desired'to have the feeding rates varying in a geometrical progression, as is frequently the case in certain machine tools. If the groove in the'plug be made helical the desired resultwill be obtained. very closely if the maximum width of slotexposed at any dial setting is an exponential function of that setting. The

area exposed thus. increases slowly at first and very rapidly as the dial settings become larger. The use of the sleeve i3 is of considerable importance' from this standpoint. For special curves such as is shown on Fig. 6 the port is best shaped witha formed tool, which is diflicult to do unless the port is in a piece such as a sleeve which. is readily accessible. Furthermore, the

provision of a portedsleeve makes it possible to secure any desired relationship between dial setring and feed rate by, choosin the proper sleeve in assembly, leaving all other parts standard. If this structure. is: used the sleeve is preferably made-in two parts It and .33 as shown in Fig. 6,

the former containing the notch forming the port I and the latter being formed as a plain cylindrical annulus. The notch is accessible from the end of the section 32 and may be formed much more readily than a hole through an integral sleeve. The sleeve portion 33 may be replaced by a shouldered part of the casing as it acts functionally only as a part of the bore; but in order to insure continuity in the surface of the bore and to permit hardening, grinding, and lapping the two part construction illustrated is preferable.

What I claim is:

A throttle valve for speed control of hydraulically operated machine tools and the like, comprising a casing having a shouldered bore, a sleeve fitting into the bore with one end against the shoulder, a plug fittin into the sleeve and provided with a circumferential flange abutting the second end of the sleeve, a cap engaging the opposite side of the flange, a port in the sleeve, a groove peripherally formed in the plug and having an axially inclined portion positioned to uncover the port progressively during the rotation of the plug, and a second port in the sleeve, said groove having a second portion positioned to connect with the second port throughout the active rotation of the plug.

FRANK W. CURTIS. 

